KR20210111728A - Positive electrode active material for secondary battery, method for preparing the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a cathode active material for a secondary battery, which comprises: a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn); and a glassy coating layer formed on a particle surface of the lithium composite transition metal oxide. The lithium composite transition metal oxide includes nickel (Ni) of which the content is 60 mol% or more among the total content of the transition metal, and manganese (Mn) of which the content is greater than the content of cobalt (Co). The glassy coating layer includes a glassy compound represented by following formula 1: Li_aM^1_bO_c. In the formula, M^1 is at least one selected from a group consisting of B, Al, Si, Ti, and P, and 1 <= a <=4, 1 <= b <= 8, 1 <= c <= 20. The present invention can improve thermal stability, reduce the residual amount of lithium by-products, and improve the particle strength of the cathode active material to prevent particle breakage during electrode rolling.

Description

Cathode active material for secondary battery, manufacturing method thereof, and lithium secondary battery comprising same

The present invention relates to a cathode active material for a secondary battery, a manufacturing method thereof, and a lithium secondary battery comprising the same.

Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

In a lithium secondary battery, an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are intercalated/deintercalated from the positive electrode and the negative electrode. Electric energy is produced by a reduction reaction with

As a cathode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _{4 ,} etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. were used. . In addition, _{as a method for improving low thermal stability while maintaining the excellent reversible capacity of LiNiO 2} , a lithium composite metal oxide in which a part of nickel (Ni) is substituted with cobalt (Co) and manganese (Mn) (hereinafter simply referred to as ‘NCM-based Lithium composite transition metal oxide') was developed. However, the conventionally developed NCM-based lithium composite transition metal oxide has insufficient capacity characteristics, so there is a limit to its application.

In order to improve this problem, recently, research to increase the content of Ni in the NCM-based lithium composite transition metal oxide is being made. However, in the case of a high-concentration nickel positive electrode active material having a high nickel content, there is a problem in that the structural stability and chemical stability of the active material are deteriorated, so that thermal stability is rapidly reduced. In addition, as the nickel content in the active material increases, _{lithium by-products present in the form of LiOH, Li 2} CO ₃ on the surface of the positive active material increase, which causes a swelling phenomenon, and the lifespan and stability of the battery are reduced There was a problem being

In addition, when the concentration of manganese (Mn) is increased to improve the thermal stability of the high-concentration nickel positive electrode active material, the particle strength of the active material is lowered, causing particle breakage during electrode rolling, which leads to deterioration of high-temperature lifespan characteristics, and high-temperature storage There was a problem with gas generation.

Korean Patent No. 10-1651338

The present invention improves the thermal stability, reduces the residual amount of lithium by-products, and improves the particle strength of the positive electrode active material in the High-Ni NCM-based positive active material containing 60 mol% or more of nickel (Ni) to secure high capacity Accordingly, an object of the present invention is to provide a cathode active material for a secondary battery that can prevent particle breakage during electrode rolling.

The present invention is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn); and a glassy coating layer formed on the particle surface of the lithium composite transition metal oxide, wherein the lithium composite transition metal oxide has a nickel (Ni) content of 60 mol% or more among the total transition metal content, and a manganese (Mn) content It is greater than the content of cobalt (Co), and the glassy coating layer provides a positive active material for a secondary battery including a glassy compound represented by the following Chemical Formula 1.

[Formula 1]

Li _a M ¹ _b O _c

In the above formula, M ¹ is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, and 1≤c≤20.

In addition, the present invention comprises the steps of preparing a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn); and dry mixing and heat-treating a coating source comprising at least one selected from the group consisting of the lithium composite transition metal oxide and B, Al, Si, Ti, and P to form a glassy coating layer; including, the lithium composite In the transition metal oxide, the content of nickel (Ni) in the total content of the transition metal is 60 mol% or more, the content of manganese (Mn) is greater than the content of cobalt (Co), and the glassy coating layer is a glassy compound represented by the following formula (1) It provides a method of manufacturing a cathode active material for a secondary battery comprising a.

[Formula 1]

Li _a M ¹ _b O _c

In the above formula, M ¹ is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, and 1≤c≤20.

In addition, the present invention provides a positive electrode and a lithium secondary battery including the positive electrode active material.

The positive active material for a secondary battery according to the present invention is a high-Ni NCM-based positive active material containing more than 60 mol% of nickel (Ni), and it is possible to secure a high capacity, and increase the concentration of manganese (Mn) to improve thermal stability while improving the glassy coating layer As a result, the particle strength can be improved. In addition, a portion of the lithium by-product present in the high-Ni lithium composite transition metal oxide may react to form a glassy coating layer, thereby reducing the lithium by-product.

In addition, when the positive electrode for a secondary battery is manufactured using the positive electrode active material according to the present invention, particle breakage during electrode rolling can be prevented, thereby improving the high-temperature lifespan characteristics of the secondary battery and suppressing gas generation during high-temperature storage have.

1 is a graph showing the results of measuring the particle strength of the positive electrode active material according to Examples and Comparative Examples.
2 is a graph showing the particle size distribution of positive active materials according to Examples and Comparative Examples after rolling.
3 is a graph showing high-temperature lifespan characteristics of secondary batteries manufactured using positive active materials according to Examples and Comparative Examples.
4 is a graph showing the amount of gas generated during high-temperature storage of secondary batteries manufactured using positive electrode active materials according to Examples and Comparative Examples.

Hereinafter, the present invention will be described in more detail to help the understanding of the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

<Anode active material>

The positive active material for a secondary battery of the present invention includes a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn); and a glassy coating layer formed on the particle surface of the lithium composite transition metal oxide.

The lithium composite transition metal oxide includes nickel (Ni), cobalt (Co) and manganese (Mn), and the content of nickel (Ni) in the total content of the transition metal is 60 mol% or more high-nickel (Ni) NCM. More preferably, the content of nickel (Ni) in the total content of the transition metal may be 80 mol% or more. When the content of nickel (Ni) in the total content of the transition metal of the lithium composite transition metal oxide is 60 mol% or more, it may be possible to secure a high capacity.

In addition, in the lithium composite transition metal oxide, the content of manganese (Mn) is greater than the content of cobalt (Co). By containing more manganese (Mn) than cobalt (Co), thermal stability can be improved. More preferably, the content of manganese (Mn) in the total content of the transition metal may be 15 to 35 mol%, more preferably 15 to 25 mol%, and the content of cobalt (Co) is 18 mol% or less, more preferably may be 5 mol% to 16 mol%.

More specifically, the lithium composite transition metal oxide may be represented by the following formula (2).

[Formula 2]

Li _p Ni _1-(x1+y1+z1) Co _x1 Mn _y1 M ² _z1 M ³ _q1 O ₂

In the above formula, M ² is at least one element selected from the group consisting of Al, Zr, B, W, Mg, Al, Ce, Hf, Ta, Ti, Sr, Ba, F, P, S and La, and M ³ is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr, 0.9≤p≤1.1, 0<x1≤0.4, 0<y1≤0.4, 0≤ z1≤0.1, 0≤q1≤0.1, x1<y1, 0<x1+y1+z1≤0.4.

In the lithium composite transition metal oxide of Formula 2, Li may be included in a content corresponding to p, that is, 0.9≤p≤1.1. If b is less than 0.9, there is a fear that the capacity may decrease, and if it exceeds 1.1, the particles are sintered in the sintering process, so it may be difficult to manufacture the positive electrode active material. Considering the remarkable effect of improving the capacity characteristics of the positive active material according to the control of the Li content and the balance of sinterability during the production of the positive active material, Li may be more preferably included in an amount of 1.0≤p≤1.05.

In the lithium composite transition metal oxide of Formula 2, Ni may be included in a content corresponding to 1-(x1+y1+z1), for example, 0.6≤1-(x1+y1+z1)<1. When the content of Ni in the lithium composite transition metal oxide of Chemical Formula 2 is 0.6 or more, the amount of Ni sufficient to contribute to charging and discharging is secured, thereby increasing the capacity. More preferably, Ni may be included as 0.8≤1-(x1+y1+z1)≤0.9.

In the lithium composite transition metal oxide of Formula 2, Co may be included in a content corresponding to x1, that is, 0<x1≤0.4. When the content of Co in the lithium composite transition metal oxide of Formula 2 exceeds 0.4, there is a risk of cost increase. Considering the significant effect of improving capacity characteristics according to the inclusion of Co, Co may be included in a content of more specifically 0<x1≤0.18, more preferably 0.05≤x1≤0.16, and may be included in an amount less than Mn. have.

In the lithium composite transition metal oxide of Formula 2, Mn may be included in a content corresponding to y1, that is, 0<y1≤0.4. When y1 in the lithium composite transition metal oxide of Chemical Formula 2 exceeds 0.4, there is a risk that the output characteristics and capacity characteristics of the battery are rather deteriorated. In consideration of the effect of improving lifespan characteristics according to the inclusion of Mn, Mn may be included in a content of 0.15≤y1≤0.35, more preferably 0.15≤y1≤0.25. In order to improve the stability of the active material and, as a result, to improve the stability of the battery, Mn may be included in an amount greater than Co.

In the lithium composite transition metal oxide of Formula 2, M ² may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ² may be included in a content corresponding to z1, that is, 0≤z1≤0.1. have.

In the lithium composite transition metal oxide of Formula 2, ^{the metal element of M 3} may not be included in the structure of the lithium composite transition metal oxide, and when the precursor and the lithium source are mixed and fired, the M ³ source is mixed and fired or , a lithium composite transition metal oxide in which ^{M 3} is doped on the surface of the lithium composite transition metal oxide can be prepared through a method of ^{separately inputting an M 3 source and sintering after forming the lithium composite transition metal oxide.} The M ³ may be included in an amount corresponding to q1, that is, a content that does not deteriorate the characteristics of the positive electrode active material within the range of 0≤q1≤0.1.

The positive active material of the present invention includes a glassy coating layer formed on the particle surface of the lithium composite transition metal oxide. The glassy coating layer includes a glassy compound represented by Formula 1 below.

[Formula 1]

Li _a M ¹ _b O _c

In the above formula, M ¹ is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, and 1≤c≤20.

When the concentration of manganese (Mn) is increased to improve the thermal stability of the high-nickel (Ni)-based positive electrode active material containing nickel (Ni) of 60 mol% or more, the particle strength is lowered, and particle breakage occurs during electrode rolling. High-temperature lifespan characteristics were deteriorated, and there was a problem of gas generation during high-temperature storage. In addition, in the case of a high-nickel (Ni)-based positive electrode active material in which nickel (Ni) is 60 mol% or more, the residual amount of lithium by-products increases, causing a swelling phenomenon, and there is a problem in that battery life and stability are reduced.

In order to solve this problem, the present invention provides a lithium composite transition metal oxide particle surface in which nickel (Ni) is 60 mol% or more high-nickel (Ni) and manganese (Mn) contains more than cobalt (Co) as described above. A glassy coating layer was formed. As such, by forming a glassy coating layer on the surface of lithium composite transition metal oxide particles containing more than 60 mol% of nickel (Ni) and high-nickel (Ni) and manganese (Mn) than cobalt (Co), thermal stability of the positive electrode active material particle strength was improved while improving In addition, a portion of the lithium by-product reacted to form a glassy coating layer, thereby reducing lithium by-products, improving high-temperature lifespan characteristics of the battery, and suppressing gas generation during high-temperature storage.

The glassy coating layer may more preferably include at least one selected from the group consisting of lithium boron oxide and lithium aluminum oxide. More preferably, lithium-boron-aluminum oxide may be included.

The glassy coating layer may contain boron and aluminum in an amount of 0.3 parts by weight: 1 part by weight to 0.8 parts by weight: 1 part by weight, and more preferably, 0.4 parts by weight of boron and aluminum: 0.4 parts by weight to 0.6 parts by weight: 1 weight. may be contained as a part. When the content ratio of boron and aluminum satisfies within the above range, particle strength may be further improved, and high temperature lifespan characteristics and high temperature storage stability may be further improved.

The glassy coating layer may be formed on the surface of the primary particles of the lithium composite transition metal oxide. The positive active material according to an embodiment of the present invention may be secondary particles formed by agglomeration of primary particles. In this case, the vitreous coating layer may be formed on the surface of the primary particles, and the vitreous coating layer is also on the surface of the secondary particles. can be formed.

The glassy coating layer may be included in an amount of 0.02 to 0.2 parts by weight, more preferably 0.04 to 0.15 parts by weight, based on 100 parts by weight of the lithium composite transition metal oxide.

The glassy coating layer may be formed to a thickness of 20 to 100 nm, and more preferably, may be formed to a thickness of 40 to 80 nm.

The positive active material of the present invention may have a particle strength of 150 MPa or more, more preferably 150 MPa to 250 MPa, and still more preferably 200 MPa to 250 MPa.

In addition, the positive active material of the present invention may have a residual lithium by-product content of 1.0 wt% or less, more preferably 0.2 to 0.8 wt%, and still more preferably 0.3 to 0.7 wt%.

<Method for producing positive electrode active material>

The cathode active material of the present invention may include preparing a lithium composite transition metal oxide including nickel (Ni), cobalt (Co) and manganese (Mn); and forming a glassy coating layer by dry mixing and heat-treating the lithium composite transition metal oxide and a coating source comprising at least one selected from the group consisting of B, Al, Si, Ti, and P.

The lithium composite transition metal oxide is a lithium composite transition metal oxide having a nickel (Ni) content of 60 mol% or more and a manganese (Mn) content greater than the cobalt (Co) content of the total transition metal content. A more specific composition of the lithium composite transition metal oxide may be applied in the same manner as described above for the positive electrode active material.

The glassy coating layer includes a glassy compound represented by Formula 1 below.

[Formula 1]

Li _a M ¹ _b O _c

In the above formula, M1 is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, and 1≤c≤20.

The glassy coating layer is formed by dry mixing and heat treatment of a coating source including at least one selected from the group consisting of B, Al, Si, Ti, and P. In this case, the lithium source may not be separately added. In the case of a high-nickel (Ni)-based lithium composite transition metal oxide containing 60 mol% or more of nickel (Ni), the residual amount of lithium by-product is large, so a part of the lithium by-product is reacted without separately adding a lithium source to form the glassy coating layer By doing so, the effect of reducing lithium by-products can also be generated. The positive active material thus formed may have a residual lithium by-product content of 1.0 wt% or less, more preferably 0.2 to 0.8 wt%, and still more preferably 0.3 to 0.7 wt%.

The coating source may include a compound containing at least one selected from the group consisting of boron (B) and aluminum (Al). For example, the coating source may be H ₃ BO ₃ , B ₂ O ₃ , HBPO ₄ , (NH ₄ ) ₂ B ₄ O ₇ , Al ₂ O ₃ , Al(OH) ₃ , Al(SO ₄ ) ₃ or Al (NO ₃ ) ₃ and the like.

The glassy coating layer may contain boron and aluminum in an amount of 0.3 parts by weight: 1 part by weight to 0.8 parts by weight: 1 part by weight, and more preferably, 0.4 parts by weight of boron and aluminum: 0.4 parts by weight to 0.6 parts by weight: 1 weight. may be contained as a part.

The coating source may be mixed in an amount of 0.02 to 2.0 parts by weight, more preferably 0.04 to 1.0 parts by weight, based on 100 parts by weight of the lithium composite transition metal oxide.

After dry mixing the coating source with the lithium composite transition metal oxide, heat treatment at 500 to 750° C. may be performed to form the glassy coating layer. The heat treatment may be more preferably performed at 600 to 700 °C.

<Anode and secondary battery>

According to another embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode active material.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may have a thickness of typically 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body, and the like.

In addition, the positive active material layer may include a conductive material and a binder together with the above-described positive active material.

In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, it may be prepared by applying the above-described positive active material and, optionally, a composition for forming a positive active material layer including a binder and a conductive material on a positive electrode current collector, followed by drying and rolling. In this case, the type and content of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent commonly used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity during application for the production of the positive electrode thereafter. do.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may specifically be a battery or a capacitor, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, a nonwoven body, and the like.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the anode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOα (0 < α < 2), SnO _{2 , vanadium oxide, and lithium vanadium oxide;} Alternatively, a composite including the above-mentioned metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite (Kish) graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

In addition, the binder and the conductive material may be the same as described above for the positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is normally used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to and excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator including a ceramic component or a polymer material may be used, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte may exhibit excellent performance.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ and the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, the electrolyte may exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions may move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle, HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium and large-sized devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

Example 1

After mixing 100 parts by weight of lithium composite transition metal oxide LiNi _0.65 Co _0.15 Mn _0.20 O _{2 and 0.29 parts by weight of H 3} BO ₃ as a coating source, heat treatment at 650° C. for 5 hours was applied to the particle surface of _{LiNi 0.65} Co _0.15 Mn _0.20 O ₂ A cathode active material having a coating layer of lithium boron oxide (LiBO ₂ , Li ₂ B ₄ O _{7 ) (B 500ppm) was prepared.}

Example 2

_{A cathode active material having a coating layer of lithium boron oxide (LiBO 2} , Li ₂ B ₄ O ₇ ) (B 1,000 ppm) was formed in the same manner as in Example 1 except that 0.58 parts by weight _{of H 3} BO ₃ was mixed as a coating source. prepared.

Example 3

A coating source H ₃ BO ₃ 0.29 parts by weight of Al ₂ O ₃ 0.22 Example 1, the same manner as the lithium, except that a mixture of parts by weight - boron-aluminum oxide _{(Li 2 B 5 AlO 10,} LiB 4 Al 7 O ₁₇ ) (B 500ppm, Al 1,000ppm) a positive electrode active material formed with a coating layer was prepared.

Comparative Example 1

A cathode active material in which a coating layer was not formed was prepared in the same manner as in Example 1 except that the coating source was not mixed.

Comparative Example 2

A cathode active material was prepared in the same manner as in Example 3 except that lithium composite transition metal oxide LiNi _0.6 Co _0.2 Mn _0.2 O _{2 was used.}

Comparative Example 3

A cathode active material was prepared in the same manner as in Example 3 except that lithium composite transition metal oxide LiNi _0.5 Co _0.2 Mn _0.3 O _{2 was used.}

[Experimental Example 1: Evaluation of particle strength]

For the positive active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the particle strength was measured by applying force by contacting the indenter with the indenter to the positive active material particles with Shimadzu MCT-W500 equipment, and the results are shown in Table 1 and FIG. 1 is shown.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Grain strength (MPa) 151.6 173.2 225.5 113.5 137.1 145.2

Referring to Table 1 and FIG. 1 , it can be seen that the particle strength of Examples 1 to 3 in which the glassy coating layer was formed compared to Comparative Example 1 in which the glassy coating layer was not formed was significantly improved. In particular, Example 3 in which the lithium-boron-aluminum oxide coating layer was formed showed a more excellent particle strength improvement effect. On the other hand, in Comparative Examples 2 and 3 in which the content of manganese (Mn) is not greater than that of cobalt (Co) or nickel (Ni) is less than 60 mol%, the particle strength is lower than in Examples 1 to 3.

[Experimental Example 2: Evaluation of residual lithium by-products]

10 g of the positive active material prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was dispersed in 100 mL of water, and then titrated with 0.1 M HCl while measuring the change in pH value to obtain a pH titration curve. The residual amount of LiOH and the residual amount of Li ₂ CO _{3 in} each positive electrode active material were calculated using the pH titration curve, and the sum of these values was evaluated as the total amount of residual lithium by-products and is shown in Table 2 below.

LiOH residual amount (wt%) Li ₂ CO ₃ Residual (wt%) Total lithium by-product residual (wt%) Example 1 0.41 0.45 0.86 Example 2 0.34 0.39 0.73 Example 3 0.26 0.33 0.59 Comparative Example 1 0.63 0.54 1.17 Comparative Example 2 0.47 0.49 0.96

Referring to Table 2, the content of residual lithium by-products was significantly reduced in Examples 1 to 3 in which the glassy coating layer was formed compared to Comparative Example 1 in which the glassy coating layer was not formed.

[Experimental Example 3: Particle Cracking Evaluation]

Each of the positive electrode active material, carbon black conductive material, and PVdF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was mixed in an N-methylpyrrolidone solvent in a weight ratio of 96.5:1.5:2 to obtain a positive electrode mixture (viscosity). : 5000 mPa·s), applied to one side of an aluminum current collector, dried at 130° C., porosity of 25%, and rolling density of 3.35 g/cm ³ to prepare a positive electrode.

After rolling, using a laser diffraction particle size measuring device (Microtrac MT 3000), ultrasonic waves of about 28 kHz with an output of 60 W were irradiated to measure the particle size distribution to evaluate the degree of particle breakage, and the results are shown in FIG. 2 .

Referring to FIG. 2 , in Comparative Example 1 in which a glassy coating layer was not formed, a lot of fine particles were formed after rolling, and a change in particle size distribution was large compared to before rolling, whereas Examples 1 to 3 in which a glassy coating layer was formed after rolling. It can be seen that the degree of generation of fine particles is reduced and the change in particle size distribution is reduced. Through this, it can be seen that Examples 1 to 3 improved the particle strength by forming the glassy coating layer.

In addition, the positive electrode was manufactured as described above, and the degree of particle breakage was evaluated by measuring the degree of contamination of the roll press through the color difference values when rolling for 200 m and 400 m compared to 0 m in the rolling section during roll press rolling, and the results are shown in Table 2 below. shown in

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Preparation before rolling
Retention (%) before rolling 100 100 100 100 100 100 200m rolling 81.6 84.3 91.4 71.7 75.5 77.1 400m rolling 74.3 80.7 90.5 57.7 61.8 65.2

Referring to Table 3, it can be seen that Examples 1 to 3 in which the glassy coating layer was formed compared to Comparative Example 1 in which the glassy coating layer was not formed had significantly reduced roll contamination. In particular, in Example 3 in which the lithium-boron-aluminum oxide coating layer was formed, it can be confirmed that the degree of roll contamination was further reduced. On the other hand, in Comparative Examples 2 and 3 in which the content of manganese (Mn) is not greater than that of cobalt (Co) or nickel (Ni) is less than 60 mol%, the degree of contamination was greater than in Examples 1 to 3. Through this, it can be seen that Examples 1 to 3 improved the particle strength by forming the glassy coating layer.

[Experimental Example 4: Battery Performance Evaluation]

Each of the positive electrode active material, carbon black conductive material, and PVdF binder prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was mixed in an N-methylpyrrolidone solvent in a weight ratio of 96.5:1.5:2 to obtain a positive electrode mixture (viscosity). : 5000 mPa·s), applied to one side of an aluminum current collector, dried at 130° C., and rolled to prepare a positive electrode.

As a negative electrode active material, natural graphite, carbon black conductive material, and PVdF binder are mixed in an N-methylpyrrolidone solvent in a weight ratio of 85:10:5 to prepare a composition for forming a negative electrode, which is applied to one side of a copper current collector Thus, an anode was prepared.

An electrode assembly was prepared by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, and the electrode assembly was placed inside the case, and then the electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving _{lithium hexafluorophosphate (LiPF 6} ) at a concentration of 1.0 M in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixed volume ratio of EC / DMC / EMC = 3 / 4 / 3) did.

Each lithium secondary battery full cell prepared as described above was charged and discharged for 100 cycles at 45° C. under the conditions of a final charge voltage of 4.25V, a final discharge voltage of 2.5V, and 0.3C/0.3C, and the capacity retention rate (Capacity Retention) [%]) was measured, and the measurement results are shown in FIG. 3 .

In addition, the amount of gas generation was measured while storing each lithium secondary battery full cell prepared as described above at 45° C. for 3 weeks, and the measurement result is shown in FIG. 4 .

Referring to FIG. 3 , it can be seen that the high-temperature lifespan characteristics of Examples 1 to 3 in which the glassy coating layer was formed compared to Comparative Example 1 in which the glassy coating layer was not formed were significantly improved. In addition, the high temperature life characteristics of Examples 1 to 3 were excellent compared to Comparative Example 2 in which the manganese (Mn) content was not greater than that of cobalt (Co) and Comparative Example 3 in which the nickel (Ni) content was less than 60 mol%. In particular, in Example 3 in which the lithium-boron-aluminum oxide coating layer was formed, it can be seen that the high-temperature lifespan characteristics were further improved.

Referring to FIG. 4 , it can be seen that the amount of gas generated during high-temperature storage of Examples 1 to 3 in which the glassy coating layer was formed compared to Comparative Example 1 in which the glassy coating layer was not formed was significantly reduced. In addition, the high temperature storage stability of Examples 1 to 3 was excellent compared to Comparative Example 2 in which the content of manganese (Mn) was not greater than that of cobalt (Co) and Comparative Example 3 in which the content of nickel (Ni) was less than 60 mol%. In particular, in Example 3 in which the lithium-boron-aluminum oxide coating layer was formed, it can be confirmed that the high-temperature storage stability is further improved.

Claims (19)

lithium composite transition metal oxide including nickel (Ni), cobalt (Co) and manganese (Mn); and a glassy coating layer formed on the particle surface of the lithium composite transition metal oxide.
In the lithium composite transition metal oxide, the content of nickel (Ni) in the total content of the transition metal is 60 mol% or more, the content of manganese (Mn) is greater than the content of cobalt (Co),
The glassy coating layer is a positive active material for a secondary battery comprising a glassy compound represented by the following formula (1).
[Formula 1]
Li _a M ¹ _b O _c
In the above formula, M ¹ is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, and 1≤c≤20.
According to claim 1,
The positive active material is a positive active material for a secondary battery having a content of residual lithium by-products of 1.0% by weight or less.
According to claim 1,
The positive active material is a positive active material for a secondary battery having a particle strength of 150 MPa or more.
According to claim 1,
The glassy coating layer is a cathode active material for a secondary battery comprising lithium-boron-aluminum oxide.
5. The method of claim 4,
The glassy coating layer is a cathode active material for a secondary battery containing boron and aluminum in an amount of 0.3 parts by weight: 1 part by weight to 0.8 parts by weight: 1 part by weight.
According to claim 1,
The lithium composite transition metal oxide is a cathode active material for a secondary battery represented by the following formula (2).
[Formula 2]
Li _p Ni _1-(x1+y1+z1) Co _x1 Mn _y1 M ² _z1 M ³ _q1 O ₂
In the above formula, M ² is at least one element selected from the group consisting of Al, Zr, B, W, Mg, Al, Ce, Hf, Ta, Ti, Sr, Ba, F, P, S and La, and M ³ is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, W and Cr, 0.9≤p≤1.1, 0<x1≤0.4, 0<y1≤0.4, 0≤ z1≤0.1, 0≤q1≤0.1, x1<y1, 0<x1+y1+z1≤0.4.
According to claim 1,
The lithium composite transition metal oxide is a cathode active material for a secondary battery in which the content of nickel (Ni) in the total content of the transition metal is 80 mol% or more.
According to claim 1,
The positive active material for a secondary battery in which the glassy coating layer is formed on the surface of the primary particle of the lithium composite transition metal oxide.
According to claim 1,
The glassy coating layer is a cathode active material for a secondary battery contained in an amount of 0.02 to 0.2 parts by weight based on 100 parts by weight of the lithium composite transition metal oxide.
According to claim 1,
The glassy coating layer is a cathode active material for a secondary battery formed to a thickness of 20 to 100nm.
Preparing a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co) and manganese (Mn); and
Forming a glassy coating layer by dry mixing and heat-treating a coating source comprising the lithium composite transition metal oxide and at least one selected from the group consisting of B, Al, Si, Ti, and P;
In the lithium composite transition metal oxide, the content of nickel (Ni) in the total content of the transition metal is 60 mol% or more, the content of manganese (Mn) is greater than the content of cobalt (Co),
The glassy coating layer is a method of manufacturing a positive electrode active material for a secondary battery comprising a glassy compound represented by the following formula (1).
[Formula 1]
Li _a M ¹ _b O _c
In the above formula, M ¹ is at least one selected from the group consisting of B, Al, Si, Ti, and P, and 1≤a≤4, 1≤b≤8, 1≤c≤20.
12. The method of claim 11,
In the step of forming the glassy coating layer, a method of manufacturing a cathode active material for a secondary battery, characterized in that not inputting a lithium source.
12. The method of claim 11,
The cathode active material is a method for producing a cathode active material for a secondary battery in which the content of residual lithium by-products is 1.0% by weight or less.
12. The method of claim 11,
The coating source is a method of manufacturing a cathode active material for a secondary battery comprising a compound containing at least one selected from the group consisting of boron (B) and aluminum (Al).
12. The method of claim 11,
The vitreous coating layer is a method for producing a positive active material for a secondary battery containing boron and aluminum in an amount of 0.3 parts by weight: 1 part by weight to 0.8 parts by weight: 1 part by weight.
12. The method of claim 11,
The coating source is a method of manufacturing a cathode active material for a secondary battery in which 0.02 to 2.0 parts by weight is mixed with respect to 100 parts by weight of the lithium composite transition metal oxide.
12. The method of claim 11,
The heat treatment is a method of manufacturing a cathode active material for a secondary battery is performed at 500 to 750 ℃.
A positive electrode for a secondary battery comprising the positive active material according to any one of claims 1 to 10.
A lithium secondary battery comprising the positive electrode according to claim 18.

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